In conventional situations the environment comprises sound fields with audio sources spread in all three spatial dimensions. The human hearing system controlled by the brain has evolved the innate ability to localize, isolate and comprehend these sources in the three dimensional sound field. For example the brain attempts to localize audio sources by decoding the cues that are embedded in the audio wavefronts from the audio source when the audio wavefront reaches our binaural ears. The two most important cues responsible for spatial perception is the interaural time differences (ITD) and the interaural level differences (ILD). For example an audio source located to the left and front of the listener takes more time to reach the right ear when compared to the left ear. This difference in time is called the ITD. Similarly, because of head shadowing, the wavefront reaching the right ear gets attenuated more than the wavefront reaching the left ear, leading to ILD. In addition, transformation of the wavefront due to pinna structure, shoulder reflections can also play an important role in how we localize the sources in the 3D sound field. These cues therefore are dependent on person/listener, frequency, location of audio source in the 3D sound field and environment he/she is in (for example the whether the listener is located in an anechoic chamber/auditorium/living room).
The 3D positioned and externalized audio sound field has become the de-facto natural way of listening.
Telephony and in particular wireless telephony is well known in implementation. Often telephony is carried out in environmentally noisy situations where background noise causes difficulty in understanding what the other party is communicating. This typically results in requests to repeat what the other party has said or stopping the conversation until the noise has disappeared or the user has moved away from the noise source. This is particularly acute in multi-party telephony (such as conference calls) where one or two participants are unable to follow the discussion due to local noise causing severe distraction and unnecessarily lengthening the call duration. Even where the surrounding or environmental noise does not prevent the user from understanding what the other party is communicating it can still be very distracting and annoying preventing the user from focusing completely on what the other party is saying and requiring extra effort in listening.
However, completely dampening or suppressing the environmental or live noise is not desirable as it may provide an indication of an emergency or a situation requiring the user's attention more than the telephone call. Thus active noise cancellation can unnecessarily isolate the user from their surroundings. This could be dangerous where emergency situations occur near to the listener as it could prevent the listener from hearing warning signals from the environment.